1a.Objectives (from AD-416):
Objective 1: Develop adapted potato clones with enhanced resistance to major potato diseases. Sub-objective 1.A. Characterize the molecular genetic basis for late blight (Phytophthora infestans) resistance in the diploid potato species Solanum bulbocastanum. Sub-objective 1.B. Identify resistance genes/factors present within late blight resistant accessions of the diploid wild potato species Solanum verrucosum. Sub-objective 1.C. Develop adapted potato germplasm with high levels of resistance to the fungal pathogen Verticillium dahliae and determine the genetic basis of resistance. Sub-objective 1.D. Identify sources of resistance to early blight (Alternaria solani), common scab (Streptomyces scabies), and soft rot (Erwinia spp., aka Pectobacterium spp.), and introgress them into S. tuberosum. Objective 2: Evaluate exotic potato germplasm for flavor and nutritional components, and introgress valuable genes into the cultivated potato. Sub-objective 2.A. Identify major components of flavor in potatoes and determine the range of variation for those traits in exotic potato germplasm. Relate biochemical variability to sensory analysis data. Sub-objective 2.B. Assess the genetic variability in wild Solanum species for nutritional quality traits including starch composition, antioxidant capacity, and vitamin and mineral levels. Where valuable variation exists, determine the genetic basis of the trait and begin studies to introgress useful genes into the cultivated potato. Objective 3: Examine exotic potato germplasm for resistance to low temperature sweetening and introgress valuable genes into the cultivated potato. Objective 4: Characterize molecular, physiological and environmental parameters that are determinants of potato quality, especially seed vigor and tuber processing quality.
Sub-objective 4.A. Characterize molecular and physiological changes that occur in potato tubers that cause, or are tightly linked to, the accumulation of reducing sugars. Sub-objective 4.B. Determine the genetic and physiological basis of tuber vigor across storage times and environments. Sub-objective 4.C. Characterize water relations and respiration of stored potato tubers and determine the range of variation for these parameters in wild and cultivated potatoes.

1b.Approach (from AD-416):
This project focuses on utilizing wild potato germplasm as a source of genes for traits important to potato improvement, such as disease resistance, flavor, nutritional quality, and low temperature sweetening. We will identify novel resistance to major potato diseases in wild relatives of the potato and introgress that germplasm into the cultivated potato. We will also use molecular genetics to characterize resistance mechanisms in wild species and hybrids with the cultivated potato (Objective 1). In addition, we will screen wild and cultivated potato relatives for flavor and nutritional quality traits, and introgress genes for these traits into the cultivated potato. In parallel, we will determine the biochemical components that can be manipulated to improve flavor and nutrition (Objective 2). We will carry out genetic studies to determine the genetic basis of cold sweetening in wild and cultivated potatoes at the diploid level, and introgress selected germplasm into the cultivated potato (Objective 3). In addition, we will carry out studies to determine the physiological basis of tuber vigor and tuber processing quality (Objective 4). Together, the completion of these objectives will lead to the development of potato cultivars that contain increased genetic diversity, require less management and are highly marketable, leading to increased revenue for the U.S. potato industry.

3.Progress Report:
This research relates to Objective 1, Develop adapted potato clones with enhanced resistance to major potato diseases., The research has led to germplasm with resistance to Potato Virus Y (PVY), scab, Verticillium wilt, and late blight. We have identified a major quantitative trait locus (QTL) for resistance to common scab on chromosome 11 and have single-nucleotide polymorphism (SNP) markers associated with that region. Tetraploid populations have been created from the scab resistant germplasm and are being evaluated in field trials. Diploid populations segregating for resistance to Verticillium wilt and PVY have been generated and are being evaluated for agronomic quality and the presence of resistance markers. Five SNP markers associated with PVY resistance have been identified on chromosome 9 and molecular marker development is underway. We have characterized the molecular interactions that determine resistance to late blight mediated by the RB resistance gene. Pathogen molecules that elicit or suppress resistance have been identified, leading to new research targeted toward improving durability of RB resistance.

This research relates to objective 2, Evaluate exotic potato germplasm for flavor and nutritional components, and introgress valuable genes into the cultivated potato. We have characterized flavor, starch, and antioxidant levels in a wide range of germplasm. We determined that both environment and genotype contribute significantly to baked potato flavor. We have evaluated a set of 322 varieties for tuber starch amylose content and provided the data to the National Research Support Program (NRSP)-6 Potato Gene Bank. We have carried out flavor, amylose, and antioxidant assays of specialty potato varieties grown in organic fields for three years. A high amylose wild species clone has been crossed with an inbred line and the resulting population is being used for the development of recombinant inbred lines for genetic studies. We determined that different preparation methods can be used to retain or reduce the amount of potassium in boiled potatoes.

This research relates to Objective 3, Examine exotic potato germplasm for resistance to low temperature sweetening and introgress valuable genes into the cultivated potato. We have identified genomic regions associated with cold-induced sweetening in wild and cultivated potato germplasm. In a diploid F2 population, two major QTL for resistance to low temperature sweetening have been identified on chromosomes 4 and 6. SNPs associated with those loci are being used for marker development. Multiple accessions from a range of wild potato relatives were screened for low temperature sweetening resistance. Resistance in one, Solanum pinnatisectum, was examined in detail at the molecular and biochemical levels. In a cultivated potato by S. raphanifolium population, stored tubers were evaluated for chip color along with invertase gene expression and enzyme activity. A germplasm release of five tetraploid clones with resistance to low temperature sweetening was published.

4.Accomplishments
1.
Reduction in post-harvest losses. Common scab and cold-induced sweetening are two of the main causes of post-harvest losses for the potato processing industry. The development of germplasm with resistance to common scab and cold-induced sweetening is a high priority for the potato industry. This germplasm can be used by breeders to develop resistant cultivars. ARS researchers at Madison, WI, developed a mapping population by mating two individuals from a diploid family generated by crossing the cultivated potato (Solanum tuberosum) clone US-W4 to the wild relative (S. chacoense) clone 524-8. The population was evaluated for resistance to common scab and cold-induced sweetening. A region on chromosome 11 was found to contribute to scab resistance, while chromosomes four and six were found to carry genetic regions responsible for cold-induced sweetening. Follow-up studies are being carried out to identify molecular markers that can be used by breeders in a high throughput manner to identify resistant individuals in segregating populations.